Developing countries should switch from unsustainable building practices to using alternative low-carbon building materials to reduce greenhouse gas emissions, a new UN report highlighted.

The world adds buildings equivalent to the size of Paris every five days, states the report — Building Materials and The Climate: Constructing A New Future — by the United Nations Environment Programme (UNEP), and the Yale Center for Ecosystems and Architecture.

About 37 per cent of global greenhouse gas emissions can be traced back to the built environment sector, which includes buildings, the distribution systems that supply water and electricity, and the roads, bridges, and transportation systems.

The UNEP report makes a case for “Avoid-Shift-Improve” strategies to reduce emissions. “Avoiding” emissions through circularity to ensure waste is eliminated while extending a building’s life, “Shifting” to sustainable materials, and “Improving” the production of conventional materials such as concrete, steel, aluminium, plastics, glass and bricks.

Greenhouse gas emissions from the built environment are categorised into two groups: embodied emissions and operational emissions.

Embodied emissions are all the emissions associated with the construction and demolishing of a building. They also include emissions from extraction, manufacturing, transport and on-site construction of building materials and “end-of-life” demolition or reuse.

Operational emissions are the emissions generated while maintaining the building’s indoor “comfort levels,” including by heating, cooling, lighting and electrical appliances.

Indirect operational emissions from residential buildings make up a majority of emissions (11 per cent), while embodied emissions from the use of concrete, steel and aluminium account for at least six per cent.

So far, the focus has been on operational emissions. The UNEP, however, warns that embodied carbon (the amount of carbon dioxide across the life cycle of the built environment process) is projected to surge from 25 per cent to nearly half (49 per cent) by 2050, whereas the share of operational carbon emissions will shrink due to increased adoption of renewable energy and improvement of energy-efficient buildings.

Developed countries, it adds, should focus on renovating existing and ageing building stock. Renovating a building generates 50-75 per cent fewer emissions than new construction, the report highlighted.

For new buildings, the experts call for incorporating circular design strategies such as the design for disassembly. It is a design process that enables the recovery of products, parts and materials when a building is disassembled or renovated. This can reduce greenhouse emissions by 10-50 per cent.

“Despite growing awareness, most contemporary material cycles continue to be more linear than circular. As a result, non-renewable, energy-intensive materials still supply the majority of demand,” the report reads.

The report added that a new supply-and-demand model should be developed. Tasks such as carefully dismantling buildings for storing, preparation and maintenance of second-cycle materials for resale will enable circular economies while providing job opportunities.

If G7 countries and China use recycled materials, they could reduce emissions in the material cycle of residential buildings by 80 to 100 per cent by 2050. In India, the reductions could reach 50-70 per cent, the report quotes the International Resource Panel (a scientific panel of experts that aims to help nations use natural resources sustainably).

Source: UNEP

They also state that increasing the lifetime of buildings creates significant opportunities to reduce aggregate embodied carbon.

The second principle is to switch towards properly managed bio-based materials. “To reach net zero emissions in the built environment sector, the building materials of the future will need to be procured from renewable or reusable sustainable sources wherever possible,” the report reads.

Of the available options, mass timber has emerged as an attractive alternative to carbon-intensive concrete and steel due to its potential for scalability, sustainability, strength and flexibility in mid-rise urban buildings.

Bamboo can be processed and manufactured into a variety of composite materials called engineered bamboo. This version has demonstrated structural performance similar to that of cross-laminated timber and steel.

As for the third principle “improve”, UNEP recommended electrifying and decarbonising the energy that is supplied to the production and maintenance of materials, buildings and urban infrastructure across their life cycle.

Processing of cement, the binding agent in concrete, contributes 7 per cent of global carbon emissions. Solutions such as reducing the clinker (produced from limestone and chalk)-to-cement ratio and increasing the share of cement alternatives, among others, could help in decarbonising the sector.

Another technology that could potentially be used is Carbon capture and utilisation for concrete production (CCU concrete). It is a process of removing carbon from the atmosphere and storing it within the building material itself over time

It is estimated that CCU concrete can remove 0.1 to 1.4 gigatonnes of CO2 by 2050. “However, there are conflicting opinions as to whether the benefits of increased strength and optimisation of materials will outweigh the carbon costs of capturing, transporting and incorporating the captured CO2 into concrete products,” reads the report.

Avoiding raw material extraction by promoting steel reuse and producing steel from scrap (discarded steel or steel product) can save around 60-80 per cent of energy, the report noted.

It also helps to reduce steel demand by extending building lifetimes, and switching to circular bio-based materials such as engineered timber and bamboo, it added.

Using renewable energy for aluminium production is important and producing aluminium from scrap can reduce the energy demand by 70-90 per cent.

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